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Commitb6ef167

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Introduce optimized routine for linear searches of arrays
Use SSE2 intrinsics to speed up the search, where available. Otherwise,use a simple 'for' loop. The motivation to add this now is to speed upXidInMVCCSnapshot(), which is the reason only unsigned 32-bit integerarrays are optimized. Other types are left for future work, as is theextension of this technique to non-x86 platforms.Nathan BossartReviewed by: Andres Freund, Bharath Rupireddy, Masahiko SawadaDiscussion:https://postgr.es/m/20220713170950.GA3116318%40nathanxps13
1 parent356dd2c commitb6ef167

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‎src/include/port/pg_lfind.h‎

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/*-------------------------------------------------------------------------
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*
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* pg_lfind.h
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* Optimized linear search routines.
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*
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* Copyright (c) 2022, PostgreSQL Global Development Group
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*
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* IDENTIFICATION
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* src/include/port/pg_lfind.h
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*
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*-------------------------------------------------------------------------
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*/
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#ifndefPG_LFIND_H
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#definePG_LFIND_H
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#include"port/simd.h"
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/*
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* pg_lfind32
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*
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* Return true if there is an element in 'base' that equals 'key', otherwise
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* return false.
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*/
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staticinlinebool
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pg_lfind32(uint32key,uint32*base,uint32nelem)
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{
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uint32i=0;
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/* Use SIMD intrinsics where available. */
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#ifdefUSE_SSE2
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/*
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* A 16-byte register only has four 4-byte lanes. For better
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* instruction-level parallelism, each loop iteration operates on a block
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* of four registers. Testing has showed this is ~40% faster than using a
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* block of two registers.
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*/
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const__m128ikeys=_mm_set1_epi32(key);/* load 4 copies of key */
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uint32iterations=nelem& ~0xF;/* round down to multiple of 16 */
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#if defined(USE_ASSERT_CHECKING)
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boolassert_result= false;
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/* pre-compute the result for assert checking */
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for (i=0;i<nelem;i++)
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{
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if (key==base[i])
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{
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assert_result= true;
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break;
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}
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}
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#endif
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for (i=0;i<iterations;i+=16)
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{
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/* load the next block into 4 registers holding 4 values each */
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const__m128ivals1=_mm_loadu_si128((__m128i*)&base[i]);
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const__m128ivals2=_mm_loadu_si128((__m128i*)&base[i+4]);
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const__m128ivals3=_mm_loadu_si128((__m128i*)&base[i+8]);
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const__m128ivals4=_mm_loadu_si128((__m128i*)&base[i+12]);
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/* compare each value to the key */
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const__m128iresult1=_mm_cmpeq_epi32(keys,vals1);
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const__m128iresult2=_mm_cmpeq_epi32(keys,vals2);
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const__m128iresult3=_mm_cmpeq_epi32(keys,vals3);
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const__m128iresult4=_mm_cmpeq_epi32(keys,vals4);
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/* combine the results into a single variable */
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const__m128itmp1=_mm_or_si128(result1,result2);
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const__m128itmp2=_mm_or_si128(result3,result4);
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const__m128iresult=_mm_or_si128(tmp1,tmp2);
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/* see if there was a match */
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if (_mm_movemask_epi8(result)!=0)
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{
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#if defined(USE_ASSERT_CHECKING)
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Assert(assert_result== true);
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#endif
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return true;
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}
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}
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#endif/* USE_SSE2 */
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/* Process the remaining elements one at a time. */
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for (;i<nelem;i++)
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{
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if (key==base[i])
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{
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#if defined(USE_SSE2)&& defined(USE_ASSERT_CHECKING)
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Assert(assert_result== true);
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#endif
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return true;
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}
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}
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#if defined(USE_SSE2)&& defined(USE_ASSERT_CHECKING)
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Assert(assert_result== false);
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#endif
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return false;
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}
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#endif/* PG_LFIND_H */

‎src/test/modules/Makefile‎

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test_extensions\
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test_ginpostinglist\
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test_integerset\
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test_lfind\
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test_misc\
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test_oat_hooks\
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test_parser\
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# Generated subdirectories
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/log/
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/results/
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/tmp_check/
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# src/test/modules/test_lfind/Makefile
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MODULE_big = test_lfind
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OBJS =\
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$(WIN32RES)\
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test_lfind.o
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PGFILEDESC = "test_lfind - test code for optimized linear search functions"
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EXTENSION = test_lfind
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DATA = test_lfind--1.0.sql
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REGRESS = test_lfind
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ifdefUSE_PGXS
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PG_CONFIG = pg_config
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PGXS :=$(shell$(PG_CONFIG) --pgxs)
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include$(PGXS)
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else
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subdir = src/test/modules/test_lfind
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top_builddir = ../../../..
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include$(top_builddir)/src/Makefile.global
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include$(top_srcdir)/contrib/contrib-global.mk
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endif
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CREATE EXTENSION test_lfind;
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--
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-- These tests don't produce any interesting output. We're checking that
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-- the operations complete without crashing or hanging and that none of their
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-- internal sanity tests fail.
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--
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SELECT test_lfind();
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test_lfind
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------------
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(1 row)
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CREATE EXTENSION test_lfind;
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--
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-- These tests don't produce any interesting output. We're checking that
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-- the operations complete without crashing or hanging and that none of their
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-- internal sanity tests fail.
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--
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SELECT test_lfind();
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/* src/test/modules/test_lfind/test_lfind--1.0.sql*/
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-- complain if script is sourced in psql, rather than via CREATE EXTENSION
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\echo Use"CREATE EXTENSION test_lfind" to load this file. \quit
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CREATEFUNCTIONtest_lfind()
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RETURNSpg_catalog.void
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AS'MODULE_PATHNAME' LANGUAGE C;
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/*--------------------------------------------------------------------------
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*
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* test_lfind.c
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*Test correctness of optimized linear search functions.
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*
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* Copyright (c) 2022, PostgreSQL Global Development Group
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*
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* IDENTIFICATION
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*src/test/modules/test_lfind/test_lfind.c
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*
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* -------------------------------------------------------------------------
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*/
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#include"postgres.h"
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#include"fmgr.h"
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#include"port/pg_lfind.h"
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PG_MODULE_MAGIC;
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PG_FUNCTION_INFO_V1(test_lfind);
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Datum
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test_lfind(PG_FUNCTION_ARGS)
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{
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#defineTEST_ARRAY_SIZE 135
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uint32test_array[TEST_ARRAY_SIZE]= {0};
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test_array[8]=1;
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test_array[64]=2;
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test_array[TEST_ARRAY_SIZE-1]=3;
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if (pg_lfind32(1,test_array,4))
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elog(ERROR,"pg_lfind32() found nonexistent element");
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if (!pg_lfind32(1,test_array,TEST_ARRAY_SIZE))
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elog(ERROR,"pg_lfind32() did not find existing element");
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if (pg_lfind32(2,test_array,32))
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elog(ERROR,"pg_lfind32() found nonexistent element");
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if (!pg_lfind32(2,test_array,TEST_ARRAY_SIZE))
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elog(ERROR,"pg_lfind32() did not find existing element");
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if (pg_lfind32(3,test_array,96))
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elog(ERROR,"pg_lfind32() found nonexistent element");
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if (!pg_lfind32(3,test_array,TEST_ARRAY_SIZE))
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elog(ERROR,"pg_lfind32() did not find existing element");
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if (pg_lfind32(4,test_array,TEST_ARRAY_SIZE))
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elog(ERROR,"pg_lfind32() found nonexistent element");
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PG_RETURN_VOID();
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}
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comment = 'Test code for optimized linear search functions'
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default_version = '1.0'
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module_pathname = '$libdir/test_lfind'
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relocatable = true

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